OP0011 EPITRANSCRIPTOME EDITING REPRESENTS AN ADDITIONAL LAYER OF IMMUNE-RELATED EPIGENETIC MEMORY OF MONOCYTES IN HUMAN SYSTEMIC LUPUS ERYTHEMATOSUS (SLE)
Authors: A. Banos, A. Kloetgen, K. Katsiki, A. Filia, D. Nikolopoulos, A. Tsirigos, D. Boumpas
Journal: Annals of the Rheumatic Diseases (2023)

<h3>Background</h3> Monocytes are key effector cells in human systemic lupus erythematosus (SLE). Cytokine production, antigen presentation and initiation/amplification of tissue inflammation<sup>[1]</sup> represent some of output functions of transcriptional rewiring within the inflammatory milieu of the disease. Epitranscriptome includes all functionally relevant changes to the RNA level (transcriptome), reforming RNA metabolism and fine-tuning gene expression<sup>[2]</sup>. <h3>Objectives</h3> To construct the transcriptional map of monocytes in lupus patients and impose the A-to-I base editing events as co-factor of the disease pathogenesis. <h3>Methods</h3> A cohort of 8 SLE patients (SLEDAI≥8) and 5 age/sex matched healthy volunteers was used for this study. PBMCs were obtained through Ficoll centrifugation and monocytes were isolated with CD14<sup>+</sup> magnetic bead selection. Total RNA was extracted and mRNA libraries were generated. Single-end 75-bp mRNA sequencing was performed on Illumina NextSeq 500. Differential expression analysis was performed using edgeR package. Genes with a false discovery rate of ≤0.05 and a fold change of &gt;1.5 were considered statistically significantly deregulated. Significant differentially expressed genes (DEGs) were used for pathway and gene ontology (GO) analysis using g:Profiler web-server<sup>[3]</sup>. For base editing events, JACUSA2 was utilized for base calling and list refinement was performed by the following criteria: (a) known editing sites based on REDIportal, (b) the number of reads with "G" at the putative editing site is at least 10 and (b) the editing level per sample, defined as 100 n(G)/[n(A)+n(G)], is at least 20%, (c) JACUSA2 call-2 score for differential editing between SLE and healthy was 1.5. <h3>Results</h3> Differential gene expression analysis produced a list of 764 statistically significant genes, 492 of which are upregulated and 272 downregulated. Gene enrichment analysis concluded that DEGs are participating in transcription regulation, signal transduction, regulation of immune processes and apoptosis/cell death. IL-17 signaling pathway and RNA metabolic process are part of the pathogenetic profile of lupus monocytes. Interestingly, <i>ADARB1</i>, key regulator of RNA editing, is upregulated (logFC=0.76, pval=0.018). A-to-I editing events found to be significant, contain among others <i>GDI2</i> (UTR3 region/signaling mediator), <i>ARPC2</i> (Alu region/actin polymerization) and <i>CERK</i> (UTR3 region/ inflammation) regulatory regions. A complex network of transcriptomic and epitranscriptomic alterations embeds immune-related genes and affects multiple cellular processes. <h3>Conclusion</h3> Transcriptional machinery and signal transduction molecules exhibit abnormal expression during transcriptional rewiring in monocytes of lupus patients. Our data support RNA editing as an additional player of immune-related epigenetic memory of monocytes, further integrating inflammatory cues and enhancing autoimmune identity of the disease. <h3>References</h3> [1] Steinbach F, Henke F, Krause B, et al Monocytes from systemic lupus erythematous patients are severely altered in phenotype and lineage flexibility. <i>Annals of the Rheumatic Diseases</i> 2000;59:283-288 [2] Roth SH, Danan-Gotthold M, Ben-Izhak M, Rechavi G, Cohen CJ, Louzoun Y, Levanon EY. Increased RNA Editing May Provide a Source for Autoantigens in Systemic Lupus Erythematosus. Cell Rep. 2018 Apr 3;23(1):50-57 [3] Uku Raudvere, Liis Kolberg, Ivan Kuzmin, Tambet Arak, Priit Adler, Hedi Peterson, Jaak Vilo: g:Profiler: a web server for functional enrichment analysis and conversions of gene lists (2019 update) <i>Nucleic Acids Research</i>, 2019. <h3>Acknowledgements:</h3> NIL. <h3>Disclosure of Interests</h3> None Declared.